NAME

       d.polar  - Draws polar diagram of angle map such as aspect or flow directions

KEYWORDS

       display, diagram

SYNOPSIS

       d.polar
       d.polar --help
       d.polar  [-x]  map=name   [undef=float]   [output=name]   [--overwrite]  [--help]  [--verbose]  [--quiet]
       [--ui]

   Flags:
       -x
           Plot using Xgraph

       --overwrite
           Allow output files to overwrite existing files

       --help
           Print usage summary

       --verbose
           Verbose module output

       --quiet
           Quiet module output

       --ui
           Force launching GUI dialog

   Parameters:
       map=name [required]
           Name of raster angle map

       undef=float
           Pixel value to be interpreted as undefined (different from NULL)

       output=name
           Name for optional EPS output file

DESCRIPTION

       d.polar calculates and displays a polar diagram of an angle raster map such as aspect, wind direction, or
       flow.  The input angle map orientation must be counter-clockwise (CCW) from east, and the angle map units
       must be degrees. This refers to the standard orientation of GRASS (e.g., see r.slope.aspect).

       The radius of the outer circle is defined by the total number of pixels in the map. If the polar  diagram
       does not reach the outer circle, no data (NULL) pixels were found in the map.

       The vector in the diagram indicates a prevailing direction, its length the strength of such direction. In
       case  all  angle  vectors are oriented along the same direction, the length for the vector is maximal (in
       fact it is equal to length of the most populated bin of the underlying histogram).

       As a side effect, the quality of the angle map can  be  derived  from  the  diagram.  Strong  spikes  may
       indicate  an  over-representation of the related angle(s) which happens in particular if integer maps are
       used.

NOTES

       If the output parameter is used, the diagram is generated as EPS file. If the -x flag is used  xgraph  is
       launched.  Otherwise d.polar will use d.graph to draw the plot in the current display frame.

       If  d.polar  is used on an aspect map generated by r.slope.aspect, the undef parameter should be set to 0
       to distinguish NO DATA (NULL) areas from areas where aspect is undefined (i.e. flat areas).

       Polar diagram of aspect map

EXAMPLE

       In this example, the polar diagram of the ’aspect’  angle  map  in  the  North  Carolina  sample  dataset
       location is generated:
       g.region raster=aspect -p
       d.polar aspect

XGRAPH REQUIREMENT

       Xgraph must be installed for the -x flag to function.

SEE ALSO

        d.graph, d.histogram, d.rast.arrow, r.slope.aspect

REFERENCES

       J. Hofierka, H. Mitasova, and M. Neteler (2009): Terrain parameterization in GRASS.  In T. Hengl and H.I.
       Reuter, editors, Geomorphometry: concepts, software, applications. Elsevier (DOI)

AUTHORS

       Markus Neteler, ITC-irst, Italy
       Bruno Caprile, ITC-irst, Italy
       Hamish Bowman, Otago University, New Zealand

SOURCE CODE

       Available at: d.polar source code (history)

       Accessed: Monday Apr 01 03:09:27 2024

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       © 2003-2024 GRASS Development Team, GRASS GIS 8.3.2 Reference Manual

GRASS 8.3.2                                                                                      d.polar(1grass)